Mobile communication system

ABSTRACT

A handover control is executed when a location area of the mobile station is changed. The communication channel applied is the optimum route suited for the roaming destination of the mobile station. A service controller 6 is provided in the mobile communication network, switching node information transmitters 7 are provided in switching nodes 151, 131 and 132 so as to transmit, to the service controller 6, switching node informations representing the nodes themselves. Furthermore, in the service controller 6, a memory 8 for storing the switching node informations, and a handover execution unit 9 for executing handover control are provided. When a fixed terminal 5 in an external network and the mobile station 1 are in communication, and the location area of the mobile station 1 is to changed due to roaming, the handover execution unit 9 specifies, on the basis of contents of the switching node information memory 8, the gateway conducting &amp; switching node 151 to be the node utilized for the communication channel. Then, the unit 9 issues an instruction to assign a channel from the gateway conducting &amp; switching node 151 to the subscriber switching node 132 in the location area which is the roaming destination.

TECHNICAL FIELD

The present invention relates to a mobile communication system, andespecially to handover control functions for changing channel assignmentof a mobile station when the mobile station roams from a currentlocation area to another location area.

BACKGROUND ART

It is generally known that, in a mobile communication system, eachmobile station communicates with others via a subscriber switching nodeof a current location area. When the mobile station roams from thecurrent location area to another area, the communication channel passingthrough the subscriber switching node in the current location areashould be changed over to another communication channel passing througha subscriber switching node in the location area which is the roamingdestination. The change of communication channels is executed byso-called handover control. The handover control adopted forconventional mobile communication systems will be described below.

FIG. 9 shows an example configuration of a mobile communication networkin which a fixed terminal 5 and a mobile station 1 communicate with eachother. In FIG. 9, all the nodes in the fixed network side are omittedwith exception of the fixed terminal. The fixed network and the mobilecommunication network are connected via a POI(i.e., point ofinterconnection) in the way of the interface point. A gateway conducting& switching node 51, being connected with other networks via the POI 4,is further connected with subordinate conducting & switching nodes 41and 42. The conducting & switching node 41 is further connected with asubscriber switching node 31 controlling a location area 21. Theconducting & switching node 42 is further connected with a subscriberswitching node 32 controlling another location area 22.

The nodes 31, 32, 41, 42 and 51 and the POI 4 are previously appendedwith identifications so called routing numbers RN. The routing numbersare assumed to be RN1 to RN6. Furthermore, the nodes and the POI 4 areconnected via channels 61 to 66. The nodes 31, 32, 41, 42 and 51 and thePOI 4 stores routing tables, respectively, as shown in followingTable-1.

                  TABLE 1                                                         ______________________________________                                        Routing tables                                                                node 31 node 32  node 41  node 42                                                                              node 51                                                                              POI 4                                 ______________________________________                                        RN1: -- RN1: 62  RN1: 61  RN1: 64                                                                              RN1: 63                                                                              RN1: 66                               RN2: 61 RN2: --  RN2: 64  RN2: 62                                                                              RN2: 65                                                                              RN2: 66                               RN3: 61 RN3: 62  RN3: --  RN3: 64                                                                              RN3: 63                                                                              RN3: 66                               RN4: 61 RN4: 62  RN4: 64  RN4: --                                                                              RN4: 65                                                                              RN4: 66                               RN5: 61 RN5: 62  RN5: 63  RN5: 65                                                                              RN5: --                                                                              RN5: 66                               RN6: 61 RN6: 62  RN6: 63  RN6: 66                                                                              RN6: 66                                                                              RN6: --                               ______________________________________                                    

The routing tables in Table-1 show the correspondence between nodes inthe routing destinations and the channels to be selected. The uses ofthe tables will be described more specifically. First, if a callconnection request for the fixed terminal 5 is originated from themobile station 1, the call connection request is judged, in thesubscriber switching node 31, to be forwarded to the POI 4.Consequently, in the subscriber switching node 31, the line "RN6" in thecorresponding routing table is referred. The numeral "61" is storedthere, so that the call connection request is further forwarded to theconducting & switching node 41 via the channel 61.

Then, in the conducting & switching node 41, the line "RN6" in therouting table stored in the node 41 is referred. The numeral "63" isstored there, so that the call connection request is further forwardedto the gateway conducting & switching node 51 via the channel 63.Similarly, the line "RN6" is referred in the gateway conducting &switching node 51. The numeral "66" is stored there, so that the callconnection request is forwarded via the channel 66. As such, the callconnection request originated from mobile station 1 is forwarded to thePOI 4 via the channels 61, 63 and 66. Then, if the fixed terminal 5 isin communicatable condition, call set up and communication are executedbetween the mobile station 1 and the fixed terminal 5.

FIG. 10 shows an example of channel connection, executed by the handovercontrol, between switching nodes in the mobile communication network. InFIG. 10, it is assumed that the mobile station 1 roams from the locationarea 21 to the adjacent location area 22, so that a handover control isrequired in order to change the subscriber switching node forcontrolling the mobile station. In this case, the subscriber switchingnode 31 controlling the location area 21 specifies, by means ofconventional processes, a subscriber switching node (e.g. the subscriberswitching node 32 in FIG. 10) which controls the location area 22 whichis the handover destination.

Then, the subscriber switching node 31 keeps the connection of channelfrom the gateway conducting & switching node 51 to subscriber switchingnode 31, namely, the channel 63 between the gateway conducting &switching node 51 and conducting & switching node 41 and the channel 61between the conducting & switching node 41 and the subscriber switchingnode 31, while setting up a channel from the subscriber switching node31 to the subscriber switching node 32 which is the handoverdestination. Then, when the channel assignment is completed, thechannels toward the subscriber switching node 32, namely, the channel 61between the subscriber switching node 31 and the conducting & switchingnode 41, the channel 64 between the conducting & switching node 41 andthe conducting & switching node 42, and the channel 62 between theconducting & switching node 42 and the subscriber switching node 32 areconnected. The handover control described above enables the mobilestation 1 to communicate via the subscriber switching node 32 of thelocation area 22 which is the roaming destination.

As described above, in the conventional mobile communication system,when the handover control due to the roaming of mobile station 1 isexecuted, the channel from the gateway conducting & switching node tothe subscriber switching node (the channel between the switching nodes51 & 41 and the channel between the switching nodes 41 & 31 in theexample of FIG. 10) is left connected, while a routing is executed fromthe subscriber switching node in which the handover originated to thesubscriber switching node in the location area which is the roamingdestination. Therefore, in view of the entire mobile communicationnetwork, application of the conventional technique is problematical, tothe mobile station 1, an inefficient channel passing through thesubscriber switching node 31, even though the channel being the optimumroute, the route consists of the channel between the switching nodes 51& 42 and the channel between the switching node 42 & 32, is existing.Furthermore, in addition to the circumstance described above, thehandover control may be executed if mobile stations communicate witheach other in a common mobile communication network and if the locationarea of either one is changed due to roaming. In this case, a problemquite similar to above will occur by the handover control.

DISCLOSURE OF INVENTION

It is accordingly, an object of the present invention to provide amobile communication system for applying an optimum route, the routesuited for the location of the mobile station, as the communicationchannel for the roamed mobile station.

The present invention provides a service controller in the mobilecommunication network, and provides switching node informationtransmitters for transmitting, to the service controller, switching nodeinformations representing the switching nodes themselves. The servicecontroller includes a switching node information memory for storing theswitching node informations which are transmitted by the switching nodeinformation transmitters, and a handover execution unit for executinghandover control on the basis of the contents of the switching nodeinformation memory. By using such a configuration, the present inventionprovides a solution to the above described problem.

According to a first aspect of the present invention, there is provideda mobile communication system which includes, a first node forcontrolling a first location area in which a mobile station can belocated, a second node for controlling a second location area in whichthe mobile station can be located, a third node, a plurality ofconducting & switching nodes for conducting the first to third nodes,and a handover controller for changing a condition of a communicationchannel assigned for the mobile station if the mobile station roamsbetween the first and second location areas, the improvement comprising:

a first switching node information transmitter for transmitting, whenthe third node and the mobile station are connected to each other viathe first node, a switching node information representing the firstnode;

a second switching node information transmitter for transmitting, whenthe third node and the mobile station are connected to each other viathe second node, another switching node information representing thesecond node;

a switching node information memory for storing either of switching nodeinformation supplied thereto; and

a handover control unit for commanding, on the basis of the switchingnode information stored in the switching node information memory, ahandover so as to assign a channel which connects the third node witheither first or the second nodes and not with one another;

whereby a channel which connects the second node and the third node andwhich does not pass through the first node is assigned.

According to a second aspect of the present invention, there is provideda method for handover utilized for a mobile communication system whichincludes, a first node for controlling a first location area in which amobile station can be located, a second node for controlling a secondlocation area in which the mobile station can be located, a third node,a plurality of conducting & switching nodes for conducting the first tothird nodes, and a handover controller for changing a condition of acommunication channel assigned for the mobile station if the mobilestation roams between the first and second location areas, theimprovement comprising the steps of:

locating the mobile station in the first location area; assigning afirst channel, between the mobile station and the third node, whichpasses through the first node and does not pass through the second node;

leaving the mobile station roaming into the second location area;

transmitting a switching node information representing the second node;

storing the switching node information into the switching nodeinformation memory;

assigning, on the basis of the switching node information stored in theswitching node information memory, a second channel, between the mobilestation and the third node, which passes through the second node anddoes not pass through the first node; and

releasing the first channel.

The third node is preferably embodied by a gateway conducting &switching node for communicating with an external network, or asubscriber switching node similar to first and second subscriberswitching nodes.

According to the former embodiment, a terminal in the external networkand the mobile station in the mobile communication network communicateswith each other. When the location area of the mobile station is changeddue to roaming of the mobile station, a channel assignment starting fromthe gateway conducting & switching node which is an interface of theexternal network can be executed.

According to the latter embodiment, the mobile stations in a commonmobile communication network communicate with each other. When alocation area of either mobile station is changed due to roaming, achannel assignment is executed from the subscriber switching node of thelocation area of another mobile station to the subscriber switching nodeof the location area which is the roaming destination of the roamedmobile station.

As such, according to the present invention, since the optimum route inthe mobile communication network is selected for the channel concerningthe handover destination, the redundant channels between the subscriberswitching node and conducting & switching node and between the pluralityof conducting & switching nodes, which are required for the conventionalhandover, can be eliminated.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a configuration of the mobile communication systemaccording to a first embodiment of the present invention.

FIG. 2 shows an example of channel connection at the beginning of thecommunication according to the first embodiment.

FIG. 3 shows an example of channel connection according to the firstembodiment when the handover takes place.

FIG. 4 shows a sequence diagram of an operation sequence of the firstembodiment at the beginning of the communication.

FIG. 5 shows a sequence diagram of an operation sequence of the handovercontrol according to the first embodiment.

FIG. 6 shows a configuration of the mobile communication systemaccording to a second embodiment of the present invention.

FIG. 7 shows an example of channel connection at the beginning of thecommunication between the mobile stations according to the secondembodiment.

FIG. 8 shows an example of channel connection according to the secondembodiment when the handover control between the mobile stations takesplace.

FIG. 9 shows a configuration of a conventional mobile communicationsystem.

FIG. 10 shows an example of channel connection of the conventionalmobile communication system when the handover takes place.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring to the drawings, the preferred embodiments of the presentinvention will be described.

<First embodiment>

FIG. 1 shows a configuration of the mobile communication systemaccording to a first embodiment of the present invention. In FIG. 1,components corresponding to those in FIG. 9 are attached with the samesymbols. In the first embodiment, subscriber switching nodes 131 & 132and a gateway conducting & switching node 151 are provided in place ofthe subscriber switching nodes 31 & 32 and the gateway conducting &switching node 51. In the gateway conducting & switching node 151 andthe subscriber switching nodes 131 & 132, there are provided switchingnode information transmitters 7, respectively. Furthermore, in the firstembodiment, a service controller 6, a controller having a switching nodeinformation memory 8 and a handover execution unit 9, is provided. Theservice controller 6 is connected, via a common signaling systemnetwork, with other switching nodes.

The switching node information transmitter 7 provided with eachswitching node is equipped with a device for informing, to the servicecontroller 6, a switching node information which is an identificationrepresenting the pertinent switching node. The switching nodeinformation memory 8 in the service controller 6 stores the switchingnode informations from the respective switching nodes. The handoverexecution unit 9 utilizes the switching node information stored in theswitching node information memory 8 so as to execute controls, such aschannel re-settings, when the handover request takes place.

FIG. 2 shows an example of channel connection at the beginning of thecommunication according to the first embodiment. In FIG. 2, handoverexecution unit 9 and the common signaling system network between theswitching nodes and the service controller, which do not work at thebeginning of the communication, are not shown. FIG. 4 shows a sequencediagram of an operation sequence at the beginning of the communicationin the first embodiment. Referring to the drawings, an example ofoperation of this embodiment at the beginning of the communication,namely, an example of operation in the case where a call from the fixednetwork terminates the mobile station 1, will be described.

First, in FIG. 2, a call connection request which originates in thefixed terminal 5 is transferred to the gateway conducting & switchingnode 151 via the POI 4. Then, the gateway conducting & switching node151 transfers, to the service controller 6, a switching node informationD1 representing the node 151 itself by means of the switching nodeinformation transmitter 7 Then, the service controller 6 stores thereceived switching node information in the switching node informationmemory 8.

Furthermore, when the call connection request is transferred, via theinformed conducting & switching node 41, to the subscriber switchingnode 131, the subscriber switching node 131 transfers, to the servicecontroller 6, a switching node information D2 representing the node 131itself by means of the switching node information transmitter 7. Then,the service controller 6 stores the received switching node informationinto the switching node information memory 8. Then, a channel passingthrough the switching nodes 151, 41 and 131 is assigned between thefixed terminal 5 and the mobile station 1 by means of conventionalprocesses.

As described above, accompanied wit h beginning of the communication, acombination of switching node informations of the gateway conducting &switching node and the subscriber switching node, the nodes which are onthe channel assigned between the fixed terminal 5 and the mobile station1 at the beginning of the communication and which are the gatewayconducting & switching node 151 and the subscriber switching node 131 inthe example described above, will be stored in the switching nodeinformation memory 8.

FIG. 3 shows an example of channel connection system in the handoverdestination when the handover control according to the first embodimenttakes place. In FIG. 3, components which do not work when the handovertakes place and the common signaling system network between theswitching nodes and the service controller are not shown. FIG. 5 shows asequence diagram of an operation sequence when the handover takes place.Referring the drawings, an example of handover operation according tothe first embodiment will be described.

In FIG. 3, when the mobile station 1 roams from the location area 21 toanother location area 22, a handover request is transferred from themobile station 1 to the subscriber switching node 131. As a result, thesubscriber switching node 131 determines the location area 22 which isthe roaming destination and a subscriber switching node 132 forcontrolling the location area 22 by means of conventional processes, andobtains a switching node information D3 thereof.

Then, the subscriber switching node 131 transmits, to the servicecontroller 6 by means of the switching node information transmitter 7,the handover request including switching node informations D4 of thenode 131 itself and of the subscriber switching node 132 which is theswitching destination.

The handover request is transferred to the handover execution unit 9 inthe service controller 6. Then, the handover execution unit 9 searches,among the combination of switching node informations stored in theswitching node information memory 8, the combination including theswitching node information (the switching node information concerningthe subscriber switching node 131 in this example) which is representingthe node handover request originated and is included in the handoverrequest. According to the example described above, a combination D5, ofswitching node informations of the gateway conducting & switching node151 and the subscriber switching node 131, is obtained as a searchedresult.

Then, the service controller 6 transmits, to the gateway conducting &switching node 151 in the combination obtained by the searching, achannel assignment command D6 which makes, the subscriber switching node132 which is the switching destination in the handover request, into theconnection destination. Furthermore, the service controller 6 stores acombined information, the information consists of switching nodeinformation of the subscriber switching node 132 in the switchingdestination and the switching node information of gateway conducting &switching node 151, as a revised information concerning the call bymeans of the switching node information memory 8.

Then, the gateway conducting & switching node 151 which has received thecommand for channel assignment executes, by means of conventionalrouting technique, a channel assignment on the basis of the switchingnode information included in the command for channel assignment. Then,the node 151 executes channel assignment toward the subscriber switchingnode 132 of the handover destination. When the new channel assignment iscompleted, the handover execution unit 9 transmits, to the gatewayconducting & switching node 151, a command D7 for switching from theprevious channel assigned at the beginning of the communication to thechannel newly assigned channel, and another command D8 for releasing theprevious channel. As a result, the gateway conducting & switching node151 executes a changeover into the newly assigned channel and releasesthe previous channel.

<Second embodiment>

In the first embodiment, communication between the fixed terminal andthe mobile station was described as an example for the mobilecommunication network and other networks. However, the present inventionis applicable even for the handover control of the communication betweenthe mobile stations within the mobile communication network. FIG. 6shows an example of configuration of the mobile communication network insuch a situation. In FIG. 6, subscriber switching nodes 131 ,132 and 133for controlling the location areas 21, 22 and 23, respectively, areconnected with conducting & switching nodes 41, 42 and 43 for conductinga plurality of switching nodes. The conducting & switching nodes 41, 42and 43 are connected to each other. As similar to the first embodiment,the switching nodes are connected with the service controller 6 via thecommon signaling system network. Furthermore, in the second embodiment,the subscriber switching nodes 131 ,132, and 133 are provided withswitching node information transmitters 7, respectively. The servicecontroller 6 is provided with the switching node information memory 8and the handover execution unit 9.

FIG. 7 shows an example of channel connection, at the beginning of thecommunication, between the mobile stations 1 and 2. In the example, achannel is assigned between the mobile stations 1 and 2 as similar tothe previous example, of communication between the fixed terminal and amobile station, with the proviso that the gateway conducting & switchingnode substitutes the subscriber switching node. FIG. 8 shows an exampleof channel connection in the handover control between the mobilestations, on the assumption that the mobile station 2 roams from thelocation area 22 into another location area 23. In another situation,wherein the location area of the mobile station 1 is changed, thehandover control can be executed in the similar process with the provisothat the mobile stations 1 and 2 are exchanged. In this situation, achannel is also assigned between the mobile stations 1 and 2 as similarto the previous example, of communication between the fixed terminal anda mobile station, with the proviso that the gateway conducting &switching node substitutes the subscriber switching node.

First, in FIG. 7, a call connection request which originates in themobile station 1 is transferred to the subscriber switching node 131.Then, the subscriber switching node 131 transfers, to the servicecontroller 6, a switching node information D1 representing the node 151itself by means of the switching node information transmitter 7. Then,the service controller 6 stores the received switching node informationin the switching node information memory 8.

Furthermore, when the call connection request is transferred to thesubscriber switching node 132 via the conducting & switching nodes 41and 42, the subscriber switching node 132 transfers, to the servicecontroller 6, a switching node information D2 representing the node 132itself by means of the switching node information transmitter 7. Then,the service controller 6 stores the received switching node informationinto the switching node information memory 8. Then, a channel betweenthe mobile stations 1 and 2 is assigned by means of conventionalprocesses. As described above, accompanied with beginning of thecommunication, a combination, of switching node informations of thesubscriber switching nodes 131 & 132 on the channel assigned between themobile stations 1 and 2, is stored in the switching node informationmemory 8.

Then, in FIG. 8, when the mobile station 2 roams from the location area22 to another location area 23, a handover request is transferred fromthe mobile station 2 to the subscriber switching node 132. As a result,the subscriber switching node 132 determines the location area 23 whichis the roaming destination and a subscriber switching node 133 forcontrolling the location area 23 by means of conventional processes, andobtains a switching node information D3 of the node 133.

Then, the subscriber switching node 132 transmits, to the servicecontroller 6 by means of the switching node information transmitter 7,the handover request including switching node informations D4 of thenode 132 itself and of the subscriber switching node 133 which is theswitching destination.

The handover request is transferred to the handover execution unit 9 inthe service controller 6. Then, the handover execution unit 9 searches,the combination including the switching node information (the switchingnode information concerning the subscriber switching node 132 in thisexample) which is representing the node handover request originated andis included in the handover request, among the combination of switchingnode informations stored in the switching node information memory 8.According to the example described above, a combination D5, thecombination of switching node informations of the subscriber switchingnodes 131 and 132, is obtained as a searching result.

Then, the service controller 6 transmits, to the subscriber switchingnode 131 the combination obtained by the searching, a channel assignmentcommand D6. The command D6 makes, the subscriber switching node 133which is the switching destination in the handover request, into theconnection destination. Furthermore, the service controller 6 stores acombined information, consisting of switching node information of thesubscriber switching node 133 in the switching destination and thesubscriber switching node 131, as a revised information concerning thecall by means of the switching node information memory 8.

Then, the subscriber switching node 131 having received the command forchannel assignment executes, by means of conventional routing technique,a channel assignment on the basis of the switching node informationincluded in the command for channel assignment. Then, the node 131executes channel assignment toward the subscriber switching node 133 ofthe handover destination. According to the channel assignment describedabove, an optimum route channel connecting the switching nodes 131, 41,43, and 133 is assigned between the subscriber switching nodes 131 and133. When the new channel assignment is completed, the handoverexecution unit 9 transmits, to the subscriber switching node 131, acommand D7 for switching from the previous channel assigned at thebeginning of the communication into the channel newly assigned, andanother command D8 for releasing the previous channel. As a result, thesubscriber switching node 131 executes a changeover into the newlyassigned channel and releasing of the previous channel.

As described heretofore, according to the second embodiment, if thehandover is to be executed when the mobile stations communicate witheach other in a common mobile communication network, since thesubscriber switching node, the node controlling the mobile station whichis not requesting the handover, executes routing originated from thenode itself and channel assignment, the channel assigned accompany withthe optimum route in the mobile communication network.

The handover control for communication between the fixed terminal andthe mobile station, and that between the mobile stations in a commonmobile communication network are described in separate embodiments;however, it will be appreciated that the present invention is notrestricted by the embodiments described above. That is, by providing allthe components described in the first and second embodiments, a unifiedmobile communication system can be composed which executes the handovercontrol described in the first embodiment when the fixed terminalcommunicates with the mobile station, and which executes the handovercontrol described in the second embodiment when the mobile stationscommunicate with each other.

We claim:
 1. A mobile communication system comprising:a first node forcontrolling a first location area in which a mobile station can belocated; a second node for controlling a second location area in whichthe mobile station can be located; a third node; a plurality ofconducting & switching nodes for conducting the first, second and thirdnodes; a handover controller for changing a condition of a communicationroute assigned to the mobile station if the mobile station roams betweenthe first and second location areas; a first switching node informationtransmitter for transmitting, when the third node and the mobile stationcommunicate with each other via the first node, a first switching nodeinformation representing the first node; a second switching nodeinformation transmitter for transmitting, when the third node and themobile station communicate with each other via the second node, a secondswitching node information representing the second node; a switchingnode information memory for storing either of said switching nodeinformation supplied thereto; and a handover execution unit forcommanding said plurality of conducting & switching nodes, on the basisof the switching node information stored in the switching nodeinformation memory, a handover so as to assign a route which connectsthe third node with either of the first or the second nodes and notconnecting the first and second nodes with one another; whereby a routewhich connects the second node and the third node and which does notpass through the first node is assigned.
 2. The mobile communicationsystem according to claim 1, wherein the third node is a gatewayconducting & switching node.
 3. The mobile communication systemaccording to claim 1, wherein the third node controls a third locationarea in which the mobile station can be located.
 4. A method forhandover in a mobile communication system which includes:a first nodefor controlling a first location area in which a mobile station can belocated; a second node for controlling a second location area in whichthe mobile station can be located; a third node; a conducting &switching network for conducting the first, second and third nodes, saidconducting & switching network including a fourth node, a fifth node, afirst channel connecting said first and fourth nodes, a second channelfor connecting said fifth and second nodes, a third channel forconnecting said third and fourth nodes without passing through saidfifth node, a fourth channel for connecting said fourth and fifth nodeswithout passing through said third node, and a fifth channel forconnecting said third and fifth nodes without passing through saidfourth node; and a handover controller for changing, in said conducting& switching network, a condition of a communication route assigned tothe mobile station if the mobile station roams between the first andsecond location areas; said handover method comprising the stepsof:locating the mobile station in the first location area; assigning afirst route, between the mobile station and the third node, wherein thefirst route passes through the first node and does not pass through thesecond node; roaming, of the mobile station, into the second locationarea; transmitting a switching node information representing the secondnode; storing the switching node information in the switching nodeinformation memory; assigning, on the basis of the switching nodeinformation stored in the switching node information memory, a secondroute, between the mobile station and the third node, which passesthrough the second node and does not pass through the first node; andreleasing the first route.
 5. The method according to claim 4, whereinthe third node is a gateway conducting & switching node.
 6. The methodaccording to claim 4, wherein the third node controls a third locationarea in which the mobile station can be located.
 7. A method forhandover according to claim 4, wherein said first route passes throughone or more channels among said third, fourth, and fifth channels, andpasses through said first channel and not with said second channel, andsaid second route passes through one or more channels among said third,fourth, and fifth channels, and passes through said second channel andnot with said first channel, if said route is assigned between saidthird node and said mobile station roams from said first location areainto said second location area.
 8. A mobile communication systemcomprising:a plurality of subscriber switching nodes, including firstand second subscriber switching nodes, for controlling location areas ofa mobile station; a third node, which is a gateway conducting &switching node connected with an external network; a conducting &switching network for conducting the first to third nodes, saidconducting & switching network including a fourth node, a fifth node, afirst channel connecting said first and fourth nodes, a second channelfor connecting said fifth and second nodes, a third channel forconnecting said third and fourth nodes without passing through saidfifth node, a fourth channel for connecting said fourth and fifth nodeswithout passing through said third node, and a fifth channel forconnecting said third and fifth nodes without passing through saidfourth node; and a handover controller for changing, in said conducting& switching network, a condition of a communication route assigned forthe mobile station if the mobile station roams from a current locationarea to another location area;wherein the mobile communication networkincludes a service controller having a switching node information memoryand a handover execution unit; the subscriber switching node and thegateway conducting & switching node are provided with switching nodeinformation transmitters, respectively, for transmitting to the servicecontroller switching node informations representing the nodesthemselves; if a communication is to be executed between the externalnetwork and the mobile station, the gateway conducting & switching nodeand the subscriber switching node, which comprise the communicationroute utilized for communication, transmit to the service controller theswitching node informations by means of the switching node informationtransmitters provided therein; the service controller stores theswitching node information into the switching node information memory;and if a handover control is required due to roaming of the mobilestation from the current location area to the another location area, thehandover execution unit in the service controller specifies, on thebasis of switching node informations stored in the switching nodeinformation memory, the gateway conducting & switching node comprisingthe communication route, and the handover execution unit causes theconducting & switching network to assign a route connecting the gatewayconducting & switching node and the subscriber switching nodecontrolling the external location area.
 9. A mobile communication systemaccording to claim 8, wherein said handover control means assign a routepassing through one or more channels among said third, fourth, and fifthchannels, and passing through said first channel and not with saidsecond channel, if said route is assigned between said third node andsaid mobile station which is visiting in said first location area, whilesaid handover control means assign another route passing through one ormore channels among said third, fourth, and fifth channels, and passingthrough said second channel and not with said first channel, if saidmobile station roams from said first location area into said secondlocation area.
 10. In a mobile communication system comprising a mobilecommunication network which includes:a plurality of subscriber switchingnodes for controlling location areas of a mobile station, saidsubscriber switching nodes including first and second nodes whichcontrol first and second location areas, respectively; a third node; aconducting & switching network for conducting the first, second andthird nodes, said conducting & switching network including a fourthnode, a fifth node, a first channel connecting said first and fourthnodes, a second channel for connecting said fifth and second nodes, athird channel for connecting said third and fourth nodes without passingthrough said fifth nodes, a fourth channel for connecting said fourthand fifth nodes without passing through said third node, and a fifthchannel for connecting said third and fifth nodes without passingthrough said fourth node; and a handover controller for changing acondition of a communication route assigned for the mobile station insaid conducting & switching network if the mobile station roams from acurrent location area to another location area;the mobile communicationnetwork includes a service controller having a switching nodeinformation memory and a handover execution unit; the subscriberswitching nodes are provided with switching node informationtransmitters, respectively, for transmitting, to the service controller,switching node informations representing the nodes themselves; if acommunication is to be executed between two mobile stations, thesubscriber switching nodes, which comprise the communication routeutilized for communication in said conducting & switching network,transmits to the service controller the switching node informations bymeans of the switching node information transmitters provided therein;the service controller stores the switching node informations in theswitching node information memory; and if a handover control is requireddue to roaming of either mobile stations from the current location areato the another location area, the handover execution unit in the servicecontroller specifies, on the basis of switching node information storedin the switching node information memory, the subscriber switching nodecontrolling the location area of another mobile station, among thesubscriber switching nodes comprising the communication route, and thehandover execution unit causes the specified subscriber switching nodeto assign a route in said conducting & switching network, said routeconnecting the specified subscriber switching node and the othersubscriber switching node controlling the location area of the othermobile station.
 11. A mobile communication system according to claim 10,wherein said handover control means assign a route passing through oneor more channels among said third, fourth, and fifth channels, andpassing through said first channel and not with said second channel, ifsaid route is assigned between said third node and said mobile stationwhich is visiting in said first location area, while said handovercontrol means assign another route passing through one or more channelsamong said third, fourth, and fifth channels, and passing through saidsecond channel and not with said first channel, if said mobile stationroams from said first location area into said second location area. 12.A mobile communication system comprising:a mobile communication networkincluding subscriber switching nodes for controlling location areas of amobile station, said subscriber switching nodes including first andsecond subscriber switching nodes which control first and secondlocation areas, respectively, a third node which is a gateway conducting& switching node connected with an external network, fourth and fifthnodes which are conducting & switching nodes for conducting theswitching nodes, a first channel connecting said first and fourth nodes,a second channel for connecting said fifth and second nodes, a thirdchannel for connecting said third and fourth nodes without passingthrough said fifth node, a fourth channel for connecting said fourth andfifth nodes without passing through said third node, and a fifth channelfor connecting said third and fifth nodes without passing through saidfourth node; a handover control means for changing a condition of acommunication channel assigned to the mobile station by changingcondition of said third, fourth or fifth channel, if the mobile stationroams from a current location area to another location area;the mobilecommunication network includes a service controller having a switchingnode information memory and a handover execution unit; the subscriberswitching node and the gateway conducting & switching node are providedwith switching node information transmitters, respectively, fortransmitting to the service controller switching node informationsrepresenting the nodes themselves; if a communication is to be executedbetween the external network and one of the mobile stations, the gatewayconducting & switching node and the subscriber switching node, whichcomprise the communication channel utilized for communication, transmitsto the service controller the switching node informations by means ofthe switching node information transmitters provided therein; theservice controller stores the switching node information in theswitching node information memory; and if a handover control is requireddue to roaming of the mobile station from the current location area tothe other location area, the handover execution unit in the servicecontroller specifies, on the basis of switching node informations storedin the switching node information memory, the gateway conducting &switching node comprising the communication channel, and the handoverexecution unit causes the gateway conducting & switching node to assigna channel connecting the gateway conducting & switching node and thesubscriber switching node controlling the external location area; and ifthe communication is to be executed between two mobile stations in themobile communication network, the subscriber switching nodes utilizedfor the communication transmit, by means of the switching nodeinformation transmitters provided therein, the switching nodeinformations to the service controller, respectively; the servicecontroller stores the switching node information into the switching nodeinformation memory; and if a handover control is required due to roamingof either of the mobile stations from the current location area to theanother location area, the handover execution unit in the servicecontroller specifies, on the basis of switching node informations storedin the switching node information memory, the subscriber switching nodecontrolling the location area of another mobile station, among thesubscriber switching nodes comprising the communication channel, and thehandover execution unit causes the specified subscriber switching nodeto assign a channel connecting the specified subscriber switching nodeand the other subscriber switching node controlling the location area ofthe other mobile station.
 13. A mobile communication system according toclaim 12, wherein said handover control means assign a route passingthrough one or more channels among said third, fourth, and fifthchannels, and passing through said first channel and not with saidsecond channel, if said route is assigned between said third node andsaid mobile station which is visiting in said current location area,while said handover control means assign another route passing throughone or more channels among said third, fourth, and fifth channels, andpassing through said second channel and not with said first channel, ifsaid mobile station roams from said current location area into saidanother location area.
 14. A mobile communication system comprising:afirst node for controlling a first location area in which a mobilestation can be located; a second node for controlling a second locationarea in which the mobile station can be located; a third node; aconducting & switching network for conducting the first to third nodes,said conducting & switching network including a fourth node, a fifthnode, a first channel connecting said first and fourth nodes, a secondchannel for connecting said fifth and second nodes, a third channel forconnecting said third and fourth nodes without passing through saidfifth nodes, a fourth channel for connecting said fourth and fifth nodeswithout passing through said third node, and fifth channel forconnecting said third and fifth nodes without passing through saidfourth node; and a handover controller for changing, in said conducting& switching network, a condition of a communication route assigned tothe mobile station if the mobile station roams between the first andsecond location areas; a first switching node information transmitterfor transmitting, when the third node and the mobile station communicatewith each other via the first node, a first switching node informationrepresenting the first node; a second switching node informationtransmitter for transmitting, when the third node and the mobile stationcommunicate with each other via the second node, a second switching nodeinformation representing the second node; a switching node informationmemory for storing either of said switching node information suppliedthereto; and a handover execution unit for commanding to said conducting& switching network, on the basis of the switching node informationstored in the switching node information memory, a handover so as toassign a route which connects the third node with either of the first orthe second nodes and not connecting the first and second nodes with oneanother; whereby a route which connects the second node and the thirdnode and which does not pass the first node is assigned.
 15. A mobilecommunication system according to claim 14, wherein said route passesthrough one or more channels among said third, fourth, and fifthchannels, and passes through either one of said first or second channelsand not with one another, if said route is assigned between said thirdnode and either one of said first or second channels.